Not Applicable
Not Applicable
1. Field of the Invention
This invention pertains generally to vehicle power trains and transmissions, and more particularly to a method and apparatus for controlling the operating characteristics of an internal combustion engine coupled to a drive train having a mechanical or electrical continuously variable transmission or a standard automatic transmission.
2. Description of the Background Art
The concept of an engine and a xe2x80x9ccontinuously variable transmissionxe2x80x9d is a very old concept invented in the 1900""s, but the theoretical efficiency of the engine, performance and driveability could never be obtained automatically. This can be seen with reference to the conventional power train and transmission shown in FIG. 1 where an internal combustion engine 10 has an output shaft 12 that drives a decoupling/starting clutch or torque converter 14, which is in turn coupled to the input shaft 16 of a continuously variable transmission (CVT) or automatic transmission (AT) 18, which in turn has an output driving a drive shaft or differential 20 coupled to a final drive wheel 22 (e. g. , axle and tire). The deficiencies of such a configuration are caused by the dynamic equation representing the engine/CVT system:             α      DS        =                                        -                          R              xc2x0                                ⁢                      I            E                    ⁢                      S            E                          +                              T            E                    ⁢          R                -                  T          loss                -                  T          RL                                      I          DS                +                              R            2                    ⁢                      I            E                                ,      
    ⁢            R      xc2x0        =                  ⅆ        R                    ⅆ        t            
where xcex1DS=acceleration of the vehicle reflected to the drive shaft,       R    =                  S        E                    S        DS              ,
IE=engine inertia, IDS=vehicle inertia at the driveshaft, SE=engine speed, SDS=drive shaft speed, TE=engine torque, Tloss=torque losses, and TRL=road load torque at the driveshaft. Because the first term xe2x88x92{dot over (R)} IESE and the second term Txcex5R generally oppose each other, the acceleration of the car and the torque and speed of the engine are difficult to control simultaneously. As a result, the best efficiency and minimum emissions for a gasoline or diesel engine cannot be realized without a sacrifice in performance. This can be seen with further reference to FIG. 2 and FIG. 3 which show operating characteristics of the engine as a function of engine speed and torque, where WOT=wide open throttle and denotes the maximum torque line, IOL=ideal torque/speed operating line and denotes where the best efficiency and/or least emissions (minimum brake specific fuel consumption or BSFC) occurs, and POL=practical operating line due to engine/transmission characteristics. Note in FIG. 3 that point A is less efficient than point B but must be used to provide proper vehicle behavior (transient performance).
The foregoing deficiencies can be overcome in accordance with the present invention by inserting an electric motor or motor/generator, a battery, and associated controls between the engine and the continuously variable or automatic transmission. It will be appreciated that when the term xe2x80x9cbatteryxe2x80x9d is used herein, the term can include any energy storage device such as an ultra capacitor, electrochemical battery, or the like.
In the preferred embodiment, a motor/generator is controlled to counteract the negative effect of thexe2x88x92 IESE in the dynamic equation. The motor/generator can then be used to allow the engine to operate at xe2x80x9cwide open throttlexe2x80x9d (WOT), or along the xe2x80x9cIdeal Torque/Speed Operating Linexe2x80x9d (IOL) for best efficiency and lowest emissions, or along any other predetermined operation line. In this way, the engine can be run continuously while energy flows into or out of the battery energy storage system connected to the electric motor/generator. If the battery is large enough to drive the vehicle a long distance, then the efficiency of energy into and out of the battery is high since the battery internal resistance is low. This concept is especially desirable for a charge depletion hybrid electric vehicle as described in my prior patent, U.S. Pat. No. 5,842,534 which is incorporated herein by reference, where the large battery pack is charged from stationary powerplants. The emissions of the gasoline or diesel engine can be controlled effectively because the engine is operated at high load consistently. The present invention ensures that the gasoline or diesel engine is never operated at closed throttle at high speeds or operated at low efficiency low load conditions. If the power required is lower than the minimum power of the engine on the IOL, the engine is automatically decoupled and stopped (or idled if desired), and the vehicle is operated as an electric vehicle.
An object of the invention is to provide for simultaneous control of the acceleration, deceleration or braking of a vehicle and the torque and speed of the engine in a vehicle.
Another object of the invention is to control the torque of the electric motor/generator to provide acceleration, deceleration and braking of a vehicle having an engine, transmission and electric motor/generator.
Another object of the invention is to allow the engine in a vehicle to always operate at wide open throttle (WOT) or along the ideal torque/speed operating line (IOL) and to vary power by engine speed.
Another object of the invention is to provide for reduced emissions of an engine by restricting its operating range.
Another object of the invention is to provide for consistently high load operation of an engine.
Another object of the invention is to achieve high vehicle acceleration and deceleration performance from a hybrid electric vehicle using a combustion engine and electric motor.
Another object of the invention is to reduce battery cycling and improve battery life in a hybrid electric vehicle.
Another object of the invention is to allow a vehicle to sustain a charge on the batteries dependent on the driving load.
Another object of the invention is to improve the efficiency of a hybrid electric vehicle.
Another object of the invention is to maximize operating efficiency of the combustion engine in a hybrid electric vehicle at varying power levels, thereby providing for betters economy.
Another object of the invention is to maximize the range of a charge depletion hybrid electric vehicle as described in my prior patent, U.S. Pat. No. 5,842,534 which is incorporated herein by reference.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.